What are SOLID principles?
💡 Concept: SOLID Principles
SOLID is an acronym representing five key principles of object-oriented design to create maintainable, scalable, and robust software.
📘 Quick Intro
The SOLID principles guide developers in designing software that is easy to maintain and extend.
🧠 Analogy
Like building blocks that fit perfectly together, SOLID principles ensure your code components are well-structured and flexible.
🔧 Technical Explanation
- S - Single Responsibility Principle: A class should have only one reason to change.
- O - Open/Closed Principle: Software entities should be open for extension but closed for modification.
- L - Liskov Substitution Principle: Derived classes must be substitutable for their base classes.
- I - Interface Segregation Principle: Clients should not be forced to depend on interfaces they don't use.
- D - Dependency Inversion Principle: Depend on abstractions, not concretions.
🎯 Use Cases
- ✅ Writing maintainable and flexible object-oriented code.
- ✅ Refactoring legacy codebases.
- ✅ Designing APIs and libraries.
- ✅ Improving unit testability.
💻 Code Example
// Example demonstrating SRP - Single Responsibility Principle
public class Invoice {
public void CalculateTotal() { /* Calculation logic */ }
}
public class InvoicePrinter {
public void Print(Invoice invoice) { /* Printing logic */ }
}
❓ Interview Q&A
Q1: What does SOLID stand for?
A: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion.
Q2: Why use SOLID principles?
A: To improve maintainability and scalability.
Q3: What is the Single Responsibility Principle?
A: A class should have only one reason to change.
Q4: What does Open/Closed mean?
A: Classes should be open for extension but closed for modification.
Q5: What is Liskov Substitution Principle?
A: Subtypes must be substitutable for their base types.
Q6: What is Interface Segregation Principle?
A: Avoid forcing clients to depend on unused interfaces.
Q7: What is Dependency Inversion Principle?
A: Depend on abstractions, not concretions.
Q8: Are SOLID principles mandatory?
A: No, but recommended for good design.
Q9: Can SOLID principles improve testability?
A: Yes, by reducing coupling.
Q10: Are these principles language-specific?
A: No, applicable across OOP languages.
📝 MCQs
Q1. What does SOLID stand for?
- Five key OOP principles
- A programming language
- A design pattern
- A framework
Q2. What is SRP?
- Single Responsibility Principle
- Solid Resource Protocol
- Systematic Refactoring Process
- Simple Reusable Pattern
Q3. What does OCP mean?
- Open/Closed Principle
- Object Control Protocol
- Operational Code Pattern
- Optional Control Process
Q4. What is LSP?
- Liskov Substitution Principle
- Logical System Process
- Link System Protocol
- Layered Software Pattern
Q5. What is ISP?
- Interface Segregation Principle
- Internet Service Provider
- Internal Service Process
- Integrated System Protocol
Q6. What is DIP?
- Dependency Inversion Principle
- Direct Implementation Pattern
- Dynamic Injection Process
- Distributed Interface Protocol
Q7. Why use SOLID?
- Maintainability and scalability
- Speed
- Compatibility
- Security
Q8. Is SOLID mandatory?
- Yes
- No
- Sometimes
- Always
Q9. Does SOLID improve testability?
- Yes
- No
- Maybe
- Rarely
Q10. Are SOLID principles language-specific?
- Yes
- No
- Sometimes
- Rarely
💡 Bonus Insight
Applying SOLID principles results in cleaner, more maintainable, and scalable object-oriented software.
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